Ever since the attention of the people in the world was drawn to the aggravating energy crisis, the trend of the development of new appliances has appeared to be chiefly oriented toward the minimization of power consumption and the enhancement of efficiency. However, conventional arc welding equipment is almost exclusively of the transformer type and is altogether unsatisfactory in view of this trend. Additionally, apart from low efficiency, conventional transformer type arc welding equipment suffers several disadvantages.
Firstly, transformers structurally involve laminated silicon steel and copper coils which render the resulting layout rather bulky and cumbersome, therefore decreasing the portability, and convenience in operation of the welding equipment. Nextly, an apparent drawback of conventional AC arc welding equipment is that the accessible range of welding is restricted to a shallow depth inward from the surface of a workpiece, and fails to reach significantly into the depth thereof. In other words, conventional equipment can only melt through relatively thin metal plate.
In welding thick plate, the processed portion of the workpiece has to be properly "shaved" to facilitate the work, otherwise, the resulting weld would be poor. At the end of welding, the previously shaved portion must be filled up with flux. This requires much labor and filler material.
Furthermore, the apparatus is always consuming power even if the arc is not at work, unless the power source is cut off. Thus in intermittant operation, the welding equipment continues to consume electricity even between two successive weld operations. Also, a considerable amount of electricity is converted into useless heat, which requires the use of fans to dissipate the heat. As a result, efficiency is rather low. This is a noticeable defect in view of the power-saving trend of the development of all facilities nowadays.
Another kind of welding equipment developed to mitigate the drawbacks of yet known AC welding equipment, namely DC welding equipment, which is provided with a bridge rectifier to allow both the positive and negative phases of alternating current applied thereto to pass in one direction, can achieve a better reach of operable depth, and by using this, the so called "shaving" can be dispensed with. However, since coil and core transformers are still used (a typical example is illustrated in FIG. 1) the size of the resulting assembly is still inconveniently large. Moreover, the undesireable continuous consumption of power during intermittant work is still inevitable.